1. Field of the Invention
The invention relates to a method for implementing EMC shielding in an electronic device, according to which method, the electromagnetic interference caused by at least one floating signal line routed across a circuit board of the device is reduced by shielding the circuit board with an electrically conductive shielding structure of the device by placing the shielding structure on a potential area on the circuit board.
The invention further relates to an arrangement used with an electronic device, which arrangement-comprises a circuit board of the device having at least one floating signal line routed across the circuit board and a potential area arranged on the circuit board, which arrangement further comprises an electrically conductive shielding structure of said device placed on the potential area.
The invention also relates to a circuit board of an electronic device, having at least one floating signal line routed across the circuit board and a potential area.
2. Brief Description of Related Developments
The increase in electronic devices, such as mobile phones, portable computers and corresponding devices, has created a need to attach more and more attention to reducing the electromagnetic interference caused by the devices in question, and to the electromagnetic interference tolerance of said devices, because the same device can both generate interfering electromagnetic radiation and be sensitive to electromagnetic interference. To improve the electromagnetic shielding, i.e. EMC shielding, devices causing interference or sensitive to interference, or their components, are shielded With at least partly electrically conductive shielding structures. For instance, to shield a component or component group which resides on the circuit board of an electronic device and causes electromagnetic interference, the component or component group in question can be surrounded by an area connected to a ground potential, and an electrically conductive protective casing or housing is arranged to it to enclose the components. The joint between the circuit board surface and the protective casing can be sealed with an electrically conductive gasket. The purpose of the protective casing is to prevent electromagnetic interference from radiating outside the casing, and also to shield the components inside the casing from outside interference. A great number of such protective casings and gaskets exist in various materials, shapes, electrical conductivity and other properties, and they are known per se to a person skilled in the art. Even the entire circuit board can be enclosed inside such a protective casing, as is done with mobile phones, for instance, in that the circuit board of the mobile phone is enclosed inside the frame and the casing of the phone, which act as a protective casing.
A known electronic device has a circuit board panel and both ends of the panel comprise edges between which the actual circuit board resides and which will be cut off at a certain stage of assembly. A system connector of the device is installed at one end of the circuit board in the area of the actual circuit board. Measurement points required for testing the operation of the circuit board are installed at the opposite end of the circuit board, on the edge of the panel. Test signal lines required for the testing have been routed between the system connector and the measurement points. After the circuit board has been tested, the edges at both ends of the panel are cut off and the cut-off test signal lines attached to the system connector at one end remain in a floating potential. Such a floating test signal line acts as an antenna and may collect both conducted and radiated electromagnetic interference from the system connector to the device and from inside the device to the system connector cables. This problem not only arises in connection with system connectors, but a corresponding problem occurs in general in any connector, having signals to be tested and attached to a circuit board, when the connector and a measurement point reside substantially on opposite edges of the circuit board or circuit board panel and floating signal lines are formed on the circuit board at some stage of the assembly. These connectors include board-to-board connectors coupling two circuit boards together, RF connectors and the like.
In another known solution, the test signal lines between the system connector and the measurement points are routed partly through the edge to be cut off from the panel on the system connector side in such a manner that when the panel edges are cut off from the actual circuit board, the direct connection between the test signal line and the system connector is cut. This solution removes problems caused possibly by conducted electromagnetic interference, but the part of the test signal line that remains floating still acts as an antenna and may collect radiated electromagnetic interference.
The object of this invention is to improve the EMC shielding of electronic devices.
The method of the invention is characterized in that during an assembly stage of a device, a shielding structure is placed at least partly oh a floating signal line in such a manner that the shielding structure connects the floating signal line to the potential area.
Further, the arrangement of the invention is characterized in that the shielding structure is placed at least partly on top of the floating signal line in such a manner that the shielding structure connects the floating signal line to the potential area.
Further, the circuit board of the invention is characterized in that the floating signal line is routed at least partly at substantially the same location as the potential area in such a manner that the shielding structure of the electronic device can at an assembly stage be arranged to the circuit board so that the shielding structure connects the floating signal line to the potential area.
The essential idea of the invention is that to improve the EMC shielding of an electronic device having an electrically conductive shielding structure and a circuit board having at least one floating signal line routed across the circuit board and a potential area, the floating signal line is at an assembly stage connected to the potential area by means of a shielding structure arranged to the circuit board in such a manner that said shielding structure of the device connects the floating signal line to the potential area. In a preferred embodiment of the invention, the shielding structure connecting the floating signal line to the potential area is the frame of the device. In a second preferred embodiment of the invention, the shielding structure has at least one part protruding inward in the shielding structure, and through this protruding part, the floating signal line is connected to the potential area. In a third preferred embodiment of the invention, the electronic device has between the potential area of the circuit board and the shielding structure of the device a gasket which connects the floating signal line to the potential area.
The invention provides the advantage that radiated electromagnetic interference, too, is reduced, and consequently, the device causes less interference to its environment and is also more interference-tolerant. Further, the operation of the device during electromagnetic interference can be better predicted. Implementing the invention also causes no additional costs.